Stepped reciprocating grates are used for the continuous conveyance and simultaneous cooling or other types of treatment of bulk materials that are deposited on the grate and to which cooling air or another treatment gas is fed from below through blower openings in the grate surface.
A plurality of grate plates located side-by-side next to each other on a grate carrier form a grate row, and a plurality of grate rows arranged one behind the other in the direction of conveyance form the grate. On reciprocating grates, individual grate rows can be moved forward and backward in the direction of conveyance, as a result of which the bulk materials carried on the grate are conveyed forward along the grate. For example, FIG. 3 of the present application displays FIG. 1 of DE 10 2004 040 048 and discloses this grate floor arrangement with a step grate of grate plates 2 (the original reference characters being modified to coincide with this disclosure). The grate plates 2 are mounted in subsequent rows on grate carriers 44. Some rows oscillate as indicated by the double headed arrow 52 for transporting bulk material on the grate floor.
“Box-like” grate plates form essentially closed, flat boxes with a top wall, a bottom wall, two side walls, a front wall and a back wall. Cooling air, for example, is fed to the grate plate through an opening in the bottom wall, the cooling air is blown into the bulk material through blower openings that are formed through the top wall.
The top walls and front walls that are in constant contact with the bulk material, in particular on the moving grate rows, are subject to a particularly high degree of wear, especially when the bulk material being transported is very hot and abrasive.
EP 0 549 816 B2 teaches that the top wall can be formed by blades of a heat-resistant and abrasion-resistant material which lie on the box which is open on top, whereby blower slots are left open between the blades. EP 0 740 766 B1 further teaches that the front wall is protected by a front plate of an appropriately resistant material fastened to it.
A particular structural problem associated with reciprocating grates of the described type are the so-called motion gaps. To prevent damage caused by friction in the area of the overlap between two grate plates that are moving relative to one another, which would produce increased wear and require increased drive power, a gap is left between the underside of one grate plate and the upper side of the successive grate plate in the direction of conveyance. This gap is generally cleared by blowing cooling air or gas through it. The gap should be configured as narrow as possible, so that the flow of air or gas that is discharged through it on the one hand, and the quantity of bulk material that falls through it on the other hand do not become uncontrollably large. An additional requirement is that the motion gap must also remain as constant as possible, even when subjected to high mechanical and thermal stresses and after extended operation, and/or it must be possible to readjust the gap easily, if necessary. Therefore, two important operating characteristics of a reciprocating grate depend on accurately calibrated motion gaps, namely the grate resistance and the amount of material passing through the gap.
The above referenced EP 0 740 766 B1 teaches that the motion gap can be adjusted by means of a vertically adjustable front plate located on the front wall. For this purpose, the front plate is provided with a slot for a fixing a bolt that extends in the vertical direction, for vertical adjustment. It became evident with this construction, on the one hand, the front plate must be welded to the adjacent front blade to permanently fix the front plate, and on the other hand, the fixing bolt must be welded to the front plate to prevent it from rotating. This requires that the blade, the front plate and the fixing bolt are made of weldable materials, which limits the choice of materials. Generally, the welding joints must also be protected against wear by cover welds. Welds are frequently defective and therefore not fail-safe. A major disadvantage of the welds is, however, that they cannot be non-destructively removed, which makes the adjustment or replacement of the front plates more difficult. Moreover, in the known design, the bolt head of the fixing bolt retaining the front plate is subjected to a high degree of wear so that after extended operation it can no longer be suitably removed with a tool.
DE 10 2004 040 048 A1 describes a vertically adjustable front plate that can be attached to the front wall, in which the threaded bolt provided for fastening the front plate or the bolt head is protected against direct contact with the bulk material by a separate cover. As shown in FIG. 3 of the present application, DE 10 2004 040 048 illustrates that the front plate 24 has an oblong hole 30, permitting adjustment of the height of the front plate 24 and thereby the height of motion gap 51 between two subsequent grate plates. The bolt head can, for example, be countersunk in a recess that is formed on the front plate 24 and protected by a cover. Here, too, it became evident that at least the cover must be welded to the front plate 24 to keep the cover in its closed position. In one embodiment, the fixing bolt 26 is prevented from rotating by flat faces formed in the inside of the cover that fit against the flats of the bolt head. However, it is necessary that the threaded bolt 26 is rotated to a specified position for the flats of the bolt head to be in line with the flanks of the cover, which is generally not corresponding with optimum pretensioning of the bolt 26.